If you want to do it in normal HTML then you always have the option of creating the Navigation area or editing it using a common Javascript document. This method is by far not the easiest, and many people don't seem to appreciate the use of Javascript, but it will work and give you the result you are after.
code:
var element = getElementById('spidnav');
element.innerHTML = element.innerHTML + '<a href="another_page.html">Click this link for yet another page to go to</a>';